PC problem (virus, not sure)?

i have a p.c problem,anytime i use my p.c,after 5 minutes it turns off just like that and my p.c fan doesn't roll/work,
this are the things i think might have been the problem,i downloaded speed fan,did some temperature shuffling,i downloaded c.cleaner(a registry cleaner,it erased a part of my anti virus and now my anti virus is turned off,but basically what i am concerned about is my fan not turning ,how can i fix this,should i re-install xp,or what ,I'm confused.please my p.c is my life.how can i make my p.c fan work please i need help.
i tried system restore,but the system restore program did not come up,i use xp on hp compaq,my p.c is about 4-5 years old and this is the first time its acting like it want's to crash
(im not sure which fan it is but it is the one by the side/under)

Yes, reinstall Windows, and be sure to download and install all the Microsoft Updates after the OS install is complete. If you have trouble installing Windows, you could have a hardware problem with the power supply, memory or the hard drive itself.

There is a fan mounted on a metal heatsink near the center of the motherboard. Is this the fan you are talking about? This fan is the CPU cooling fan. If it doesn't turn, the computer will not run for long

You didn't seem like you were very knowledgeable with computer hardware... We need to know your computers model number to tell how much the new fan and heatsink would cost. Is it also an HP? You have to remove the old heatsink and fan. Clean off the old thermal paste and apply a small amount of new thermal paste to the CPU then install the new HSF (Heatsink and fan assembly) Can you do this? If you make a mistake, you could destroy the motherboard

You have to remove the old heatsink and fan. Clean off the old thermal paste and apply a small amount of new thermal paste to the CPU then install the new HSF (Heatsink and fan assembly) Can you do this?

This is a laptop! Much harder to work on. The laptop has to be disassembled and the heatsink and fan(s) are one big assembly costing $40 to $50 on EBay, not counting the labor to reinstall the assembly